The red imported fire ant, or RIFA for short, is no ordinary red ant. This invasive pest lives up to its name, delivering a sting that causes a burning sensation when its venom is injected into the skin.

People sometimes confuse RIFA with the native southern fire ant. Both can become very agitated when their nest is disturbed but RIFA are more likely to attack. RIFA can bite and sting its victim repeatedly, and its sting is more serious, causing a burning and itching sensation. This is followed by the formation of a white pustule, which can take several weeks to disappear. If not kept clean, the pustules can become infected and may leave permanent scarring. A small...

The black widow spider is the most harmful spider in California. (Photo: Jack Kelly Clark)

Unlike mosquitoes, spiders do not seek people in order to bite them. Generally, a spider doesn't try to bite a person unless it has been squeezed, lain on, or similarly provoked to defend itself. Moreover, the jaws of most spiders are so small that the fangs cannot penetrate the skin of an adult person. Sometimes when a spider is disturbed in its web, it may bite instinctively because it mistakenly senses that an insect has been caught.

The severity of a spider bite depends on factors such as the kind of spider, the amount of venom injected, and the age and health of the person bitten. A spider bite might cause no reaction at all, or it might result in varying amounts of itching, redness, stiffness, swelling, and...